The present invention relates to a screen input type display device having a construction in which a touch panel, which detects input coordinates based on a change of resistance produced by a push manipulation, is laminated on a display device.
As an example, it is known to use a liquid crystal display device as a display means in a personal computer or as another type of monitor. This type of display device irradiates illumination light to form images on a liquid crystal panel, and it visualizes the images by irradiating transmitting light or reflection light to a display surface side.
In general, a screen input type display device which adopts this type of liquid crystal display uses a liquid crystal panel which sandwiches a liquid crystal layer in a space defined between a pair of laminated substrates having pixel selecting electrodes and the like, and it can generate images by changing the orientation state of liquid crystal molecules corresponding to selected pixel portions. Since the generated image per se is not in the visible state, the liquid crystal panel is irradiated by applying light from the outside, and transmitting light or reflection light therefrom is observed as the image.
Recently, an information terminal, which uses this type of liquid crystal display device as a display means and is provided with a touch panel, which is laminated on a screen of the liquid crystal display device and inputs various information through the screen by a push manipulation, has been widely used.
Although there exist touch panels for various systems depending on the operating principles thereof, the most popular touch panel is one which adopts a system in which input coordinates are detected depending on a change in the quantity of resistance, i.e. a so-called xe2x80x9canalogue resistance film systemxe2x80x9d.
In this touch panel based on an analogue resistance film system, one substrate, which forms an information input side, is constituted of a soft film, such as a transparent plastic sheet or the like, while the other substrate is constituted of a transparent hard plate, preferably made of glass, and the resistance films are respectively provided on opposing surfaces of the two transparent substrates. With such a construction, a two dimensional coordinate value is detected based on the resistance value between the resistance films of the respective substrates, which are brought into contact with each other in response to the push manipulation applied from one substrate side, and an output terminal.
FIG. 18 is a schematic cross-sectional view illustrating an example of an overall constitution of a screen input type display device which constitutes a display device provided with a touch panel. This display device is constituted by laminating a touch panel 100 on a liquid crystal panel 300. Although the illustrated display device is of a type which inserts an auxiliary light source device 200 between the liquid crystal panel 300 and the touch panel 100, a display device which mounts the auxiliary light source device on a side opposite to a display screen of the liquid crystal panel 300, or a display device which is not provided with an auxiliary light source device has been commercialized. In the drawing, numeral 202 indicates a lamp which constitutes an element of the auxiliary light source device 200 and numeral 203 indicates a lamp reflection sheet which also constitutes an element of the auxiliary light source device 200.
FIG. 19A and FIG. 19B are schematic cross-sectional views illustrating the constitution and the state at the time of push manipulation of an essential part of a signal input side of the touch panel shown in FIG. 18, respectively. Although the upper substrate is referred to as a first substrate and the lower substrate is referred to as a second substrate for facilitating the explanation, these substrates may be arranged up side down.
In FIG. 19A and FIG. 19B, numeral 2 indicates an upper substrate made of a transparent film, such as plastic or the like, and numeral 3 indicates a lower substrate made of a hard plate, such as a glass plate. On inner surfaces of these two substrates 2, 3, an upper resistance film 4 and a lower resistance film 5, which are respectively preferably made of ITO, are formed as a coating. Further, in an input region AR of the lower resistance film 5, which is formed on the lower substrate 3, dot-like spacers 9 which prevent upper and lower resistance films 4, 5 from coming into contact with each other in the non-input manipulation state are formed. The spacers 9 are formed by printing using a mask having given apertures, or a photolithography technique or the like using a photosensitive resin.
In an adhesion region (seal region) SL, which is located at an outermost periphery of the touch panel, the upper resistance film 4 is electrically connected to an upper wiring electrode 6, which is formed on the upper resistance film of the upper substrate, and an inter-substrate connection wiring electrode 7, which is formed on the lower substrate. The inter-substrate connection wiring electrode 7 is connected to a coordinate recognition circuit disposed outside by an outgoing line (generally, a flexible printed circuit board: FPC), which is not shown in the drawing, by way of a pull-around wiring, which is also not shown in the drawing. The lower resistance film 5, which is formed on the lower substrate 3, is connected to a lower wiring electrode, which is not shown in the drawing, and the lower resistance film 5 is connected to the outgoing line by way of a pull-around wiring, which is not shown in the drawing and is formed on the inner surface of the lower substrate 3.
The upper wiring electrode 6 and the inter-substrate connection wiring electrode 7 are respectively coated with protective films (insulation films) 12A, 12B, and these protective films are adhered to each other by means of a seal agent (adhesive agent or adhesive sheet) 13.
Toward the inside from the seal region SL, the input region AR is positioned by way of an inoperable region NR. The inoperable region NR is a portion which becomes insensitive at the time of performing the push input manipulation. As shown in FIG. 19B, this inoperable region NR corresponds to an input invalidation space which is formed when the upper substrate 2 is deflected toward the lower substrate 3 upon receiving the pressure of a nib 56, which constitutes an input means.
In general, in this inoperable region NR, an inoperable region forming member 14 is provided to prevent an input failure of information by the push input manipulation of the nib 56. That is, the inoperable region forming member 14, which has a size that ensures the entrance of the nib 56 in the input region AR in the state shown in FIG. 19B and is made of a transparent insulation material, is provided to the inoperable region NR.
FIG. 20 is a schematic cross-sectional view illustrating the constitution of an essential part of a connection portion between the upper wiring electrode 6 and the inter-substrate connection wiring electrode 7 of the touch panel. The upper wiring electrode 6 formed on the upper resistance film 4 on the inner surface of the upper substrate 2 and the inter-substrate connection wiring electrode 7 formed on the inner surface of the lower-substrate 3 are electrically connected with each other by way of an adhesive agent 14 made of epoxy resin in which metal particles are mixed.
In the conventional screen input type display device provided with a touch panel having such a constitution, conductive thin films made of silver paste or the like, which are coated on the upper and lower wiring connection portions, and an adhesive agent in which the metal particles are mixed are used; hence, when a gap between the upper and lower substrates is set to approximately 40 xcexcm to 150 xcexcm, it is difficult to control such a gap. When the gap between the upper and lower substrates is not uniform, a user has an uncomfortable feeling at the time of performing a push manipulation. This is one of problems to be solved by the present invention.
Further, since the adhesive agent 14, in which the metal particles are mixed, is used for the connection between the upper wiring electrode 6, formed on the upper resistance film 4 of the upper substrate 2, and the inter-substrate connection wiring electrode 7, formed on the lower substrate 3, irregularities are liable to be generated in the connection resistance, and it is difficult to stabilize the linearity of the detected resistance value. This brings about an erroneous operation. To reduce the occurrence of this erroneous operation, the load which a coordinate detection circuit must bear becomes large. This also has been a problem to be solved for enhancing the reliability of the screen input type display device.
Accordingly, it is an object of the present invention to provide a screen input type display device using a touch panel having a high reliability, which can solve the above-mentioned problems of the prior art, can easily perform gap control between upper and lower substrates, can stabilize the linearity of the resistance value detection with the use of the resistance films and can eliminate erroneous operation in the course of coordinate detection.
To achieve the above-mentioned object, for establishing the connection between a wiring electrode connected to a resistance film of a first substrate and an inter-substrate connection wiring electrode formed on a second substrate, the present invention adopts a planar (or tape-like) structural body which sandwiches a metal foil between conductive pressure sensitive adhesive agents, that is, a conductive pressure adhesive member in which conductive pressure sensitive adhesive agents are coated on both surfaces of a metal foil. The resistance film of the first substrate may be directly brought into contact with the conductive pressure sensitive adhesive member without interposing a wiring electrode therebetween.
Further, as conductive material contained in the conductive pressure sensitive adhesive agent, metal particles preferably made of copper particles or alternatively plastic particles or glass particles, which have a metal plating made of nickel, gold or other metal formed on the surface thereof, can be used.
With the use of the structural body having such a constitution, since the resistance film of a first substrate, or the wiring electrode which is connected to the resistance film, and the inter-substrate wiring electrode formed on the second substrate are electrically connected by a face contact, a stability of the contact resistance is achieved. Accordingly, the linearity of the resistance value detection is improved, so that erroneous coordinate detection can be obviated, and the load that a coordinate detection circuit must bear can be reduced.
Further, according to the constitution of the present invention, by changing the thickness of the metal foil, the gap between the first substrate and the second substrate (upper and lower substrates) can be arbitrarily, accurately and uniformly controlled, and the input feeling can be enhanced.
The present invention adopts a structural body (conductive pressure sensitive adhesive member) which is formed by coating pressure sensitive adhesive material, in which metal particles are mixed, on one surface of a metal foil, and coating pressure sensitive adhesive material, in which conductive particles formed by applying a metal plating on surfaces of plastic particles or conductive particles formed by applying a conductive metal plating on surfaces of glass particles, are mixed on the other surface of the metal foil.
Then, the above-mentioned one surface is made to face the first substrate in an opposed manner, and the other surface is made to face the second substrate in an opposed manner. Due to such a constitution, by making use of a collapsing or embedding of the conductive particles, the direct contact area between the conductive particles and the conductive pressure sensitive adhesive members formed on the inner surface of either one or the other substrate, or between the conductive particles and the resistance films, can be increased. Here, the formation of the wiring electrode on the first substrate side can be omitted. Further, by directly embedding the conductive particles into the wiring electrode or the resistance film formed on the inner surface of one substrate, the direct contact area can be increased and the gap can be accurately set.
The above-mentioned one substrate and the other substrate respectively constitute the first substrate and the second substrate, and either one of these substrates constitutes an input-side substrate, that is, an upper substrate of a touch panel, which becomes a product or a substrate opposite to the input-side substrate, that is, a lower substrate of the touch panel.
As a display device used as a screen input type display device according to the present invention, a liquid crystal display device which uses a liquid crystal panel of a so-called xe2x80x9cpassive matrix typexe2x80x9d, xe2x80x9cactive matrix typexe2x80x9d or other known type can be used. Further, the present invention is not limited to the reflection-type liquid crystal display device and is applicable to a transparent-type or a semitransparent/reflection type liquid crystal display device. Further, the present invention is not limited to the liquid crystal display device and is applicable to other display devices.
The constitution of the screen input type display device of the present invention, which laminates the touch panel, is not limited to the constitution specifically described in xe2x80x9cwhat is claimed isxe2x80x9d and the constitutions of embodiments which will be explained later. That is, the constitution of the screen input type display device of the present invention is also applicable to any conductive connection between a first substrate and a second substrate of a touch panel in a system which detects coordinates based on the change of capacity between the first and second substrates or change of another electric quantity or of a digital system. In this manner, various modifications are conceivable without departing from the technical concept of the present invention.